The invention discloses an oil exploitation method for an ultra-low-permeability water-sensitive reservoir/tight reservoir. The oil exploitation method comprises the following steps that after cased hole completion of a horizontal well in an ultra-low-permeability or tight oil deposit area, a horizontal well staged fracturing technology is adopted for carrying out staged fracturing on the reservoir to form N artificial fractures communicated with the horizontal well, and the Mth artificial fracture is closer to a well mouth of the horizontal well than the (M+1)th artificial fracture. A horizontal section, between the first artificial fracture and the second artificial fracture adjacent to the first artificial fracture, of the horizontal well is subjected to setting, carbon dioxide is injected into the first artificial fracture through a sleeve pipe, oil exploitation is carried out through an oil pipe, and deblocking is carried out after oil exploitation is completed. A horizontal section, between the Mth artificial facture and the (M+1)th artificial fracture adjacent to the Mth artificial fracture, of the horizontal well is subjected to setting, and after carbon dioxide is injected into the Mth artificial fracture through the sleeve pipe, oil exploitation is carried out through the oil pipe. By means of the method, carbon dioxide injection and oil exploitation in the same well can be achieved through one horizontal well.